In a medium-sized saucepan, combine brown sugar, Karo syrup, vanilla and 1 cup of water. Bring to a boil and then turn to low and allow to reduce until slightly thickened. Stir in salt and allow to cool completely.
In order to see how sweet you like it, mix a 1:1 ratio simple syrup to bourbon. If you like it sweeter, combine 2 parts syrup to bourbon.
Top drink with a small amount of additional salt if desired. Serve warm or over ice.
This recipe was calculated using the exact brands and measurements I used to make this recipe. If you are following a strict diet please note changing anything will cause the nutritional info to change. My calculations are intended as a guide only.